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Smart Bridges

This video segment adapted from NOVA scienceNOW features two engineering innovations designed to improve structural safety in bridges. The video shows how sound waves can be used to detect cracks in steel and other signs of bridge instability undetected by the human eye. A second approach involves painting onto the bridge a "sensing skin" made of microscopic carbon nanotubes that use electrical currents to reveal structural damage or weak spots. This resource is useful for introducing components of Engineering Design (ETS) from the Next Generation Science Standards (NGSS) to grades 6-12 students.

This video is available in both English and Spanish audio, along with corresponding closed captions.

This video explains an Engineering Design problem: There has not been an easy way to determine whether or not a bridge is structurally sound. Two potential solutions are presented in detail.

After watching the video: Ask students to identify the problem addressed in the video. Do they agree that it’s an issue? This activity helps students articulate the specific problem that needs to be addressed, part of the Engineering Practice, Defining Problems.

The video presents two potential solutions. Ask students to discuss the pros and cons of each solution. Which of the solutions would they choose and why? This part of the activity helps students evaluate competing design solutions, part of the Engineering Practice, Engaging in Argument from Evidence.

When evaluating solutions, it is important to take into account a range of constraints, including cost, safety, reliability, and aesthetics, and to consider social, cultural, and environmental impacts.

Engineering Practice: Designing Solutions

This video explains an Engineering Design problem: There has not been an easy way to determine whether or not a bridge is structurally sound. Two potential solutions are presented in detail.

After watching the video: Ask students to identify the problem and the potential solutions presented in the video. Have them discuss the pros and cons of each solution. Make sure that they are considering a range of constraints, including cost, safety, reliability, and aesthetics, and to consider social, cultural, and environmental impacts. Which of the solutions would they choose and why? This activity helps students evaluate solutions based on scientific knowledge, student-generated sources of evidence, prioritized criteria, and tradeoff considerations, part of the Engineering Practice, Designing Solutions.

While safety inspections are a routine part of building, bridge, and airplane maintenance, structural problems can be missed because inspectors still rely heavily on their eyes to detect them. This means that a flaw below the surface or one too small to be seen may go completely unnoticed. As most structural failures stem from minute cracks that grow over time and use, early detection is essential to ensure safety.

Several new technologies have emerged from a new approach in engineering called structural health monitoring. Two examples of these sensor-based systems—both featured in this video segment—include an acoustic wave system, which is similar to sonar, and carbon nanotube paint, an innovation still in development that uses electrical currents to detect flaws.

An acoustic wave system uses sound to collect critical data about structural elements. Employing a network of electrical patches placed along the structure's surface, this system can signal defects before small problems become catastrophic. Any of the patches can emit a "ping" of high-frequency sound waves from its location. As with sonar, the waves bounce off objects they bump into and return to their source. As this happens, the patch switches to sensor mode and "listens" to the returning signal or sound echo. This echo contains information that, when interpreted by pattern-recognition software connected to the sensor, attests to the integrity of the structure over the test area. If the return time varies from a previous reading obtained during an earlier inspection, the sound wave's path has been altered somewhere in the structural material. In a bridge, this could suggest that the steel contains a defect, such as a crack or corrosion, between two monitoring points. Besides buildings, bridges, and airplanes, this technology can also be used to monitor the structural health of spacecraft, pipelines, ships, and power plants.

Researchers are also developing a coating they can use to generate images of faults in structural components. This opaque "sensing skin" contains microscopic cylindrical carbon structures called carbon nanotubes. Electrical current is sent through the conductive skin from electrodes implanted along the perimeter of the painted area, and a computer monitors the results. When electrical current flows through a material, it encounters resistance: a measure of how much the flow of electric charge is opposed by the material. Any changes in the electrical resistance in the nanotube skin suggest the presence of a crack or other defect beneath the painted layer. The bigger a defect is, the higher the electrical resistance will be. Thus, using the collected data, the computer can visualize the resistance and generate a two-dimensional image for an inspector to review. With the push of a button, an inspector could receive a map of any area covered with the skin, and problems, no matter how small, could be pinpointed.